Dishwashing machines (warewashers), in particular commercial dishwashing machines, in the form of box-type dishwashing machines (box-type warewashers) may be hood-type dishwashing machines (hood-type warewashers) or frontloaders (frontloader warewashers).
A dishwashing machine (box-type warewasher) and a plurality of methods for the operation thereof are known, for example, from WO 2006/129963 A2. Said dishwashing machine is provided with a steam generator for treating the washware with steam during various process cycles. The use of steam is provided before a washing cycle or after a washing cycle. Treating washware with steam between a prewash cycle and a main wash cycle is also known from DE 29 00 954 A1.
EP 0 808 894 B1 discloses a method according to which the washware is sprayed with detergent solution (detergent) during a prewash cycle, before a main wash cycle and, following this, a final rinse cycle then take place. Spraying washware with a highly concentrated alkaline detergent solution is also known from EP 1 347 039 B1.
WO 2006/037447 A1 discloses a dishwashing machine in which washware is washed with washing liquid, then rinsed with fresh water, and then subjected to thermal aftertreatment with steam.
Since washware normally includes not only tableware, for example plates and cups, but also cutlery, for example spoons, forks and knives, and also other utensils, for example trays, pots and pans, dishwashing machines, in particular commercial dishwashing machines, are also called utensil washers (warewashers).
Commercial dishwashing machines or utensil washers normally operate in two main process steps: a 1st step which includes washing with a washing liquid, and a 2nd step which includes final rinsing with heated fresh water and the metered addition of a final rinse aid.
In order to be able to carry out these process steps, a commercial dishwashing machine is generally equipped with two independent liquid systems which are completely separate from one another. One of the liquid systems is a washing water circuit which is responsible for washing the washware, with washing being carried out using recirculated water from a washing tank. The other liquid system is a fresh water system which is responsible for final rinsing. Final rinsing is carried out with fresh water, preferably with fresh water from a water heater (boiler). The fresh water is likewise held by the washing tank after being sprayed.
The main objective of final rinsing is to remove washing liquor from the washware. In addition, the final rinse water which flows into the washing tank during the final rinse step serves to regenerate the washing water which is present in the washing tank.
Before fresh water is sprayed and thus conducted into the washing tank as final rinse liquid as a result of final rinsing, a quantity of washing liquid which is equal to the quantity of fresh water is pumped out of the washing tank.
Modern dishwashing machines are equipped with a plurality of programs. These programs differ mainly by virtue of program run times of the washing process step of different lengths. The customer has the option of selecting a short washing program for washware which is lightly soiled, or of selecting a correspondingly longer washing program for washware which is heavily soiled.
The proportion of washware which is heavily soiled, for example contains burnt-on food residues, is frequently very high, particularly in the case of commercial dishwashing machines or utensil washers. Since cookware, heat-retaining boxes or baking tins and baking trays with burnt-on food residues, for example, are washed in dishwashing machines of this type, such washware is prewashed or postwashed in many cases since “normal” machine washing is not able to provide a satisfactory wash result, even with relatively long run times of the programs.
The object of the invention is to provide an option by means of which the wash process can be shortened in an ergonomical and environmentally friendly manner.